Saturn is the most spectacular planet in the solar system to view through a telescope. Many astronomers would agree that it provides the most beautiful view of any celestial object in a telescope. Saturn’s rings steal the show. They are composed of a myriad of icy particles, each following its own orbit around Saturn. The particles range in size from smaller than a pea- to house-sized boulders. Since Saturn is almost 10 A.U. from the Sun, the particles are cold - much less than 100 Kelvins, or about 400 below zero Farenheit. This makes them hard as rock. The particles are grouped into many separate rings that surround the planet. Only three of these rings are visible from Earth-bound telescopes. They are labeled as the A, B, and C rings. The A and B rings are the outermost and brightest of the big rings, and are separated by a dark gap called Cassini’s Division. Look for Cassini’s Division in the telescope as a thin, black line separating the outer A ring from the middle B ring. The inner Crepe, or C ring is an extremely thin ring that is visible from Earth only under the best conditions. If you have a very good telescope, great conditions, and a good eye, you may be able to spot this ring inside the bright B ring as a thin veil of ring material that circles the planet.

Saturn itself is a gas giant and the second largest planet in the solar system. It displays visible belts (dark "stripes") and zones (white stripes). Saturn is the least dense planet in the solar system, less dense than water. It also is the second-fastest rotator. A Saturnian day lasts a mere 10 hours and 55 minutes. The low density and rapid rotation combine to make Saturn the most oblate planet in the solar system. Look for this in the telescope. Note that Saturn looks "squashed".

Saturn has a very interesting satellite system. It has one very large satellite and the most medium-sized moons of any planet in the solar system. Titan is the big moon. It is larger than the planet Mercury. It is the only satellite in the solar system to possess a thick atmosphere. Titan’s atmosphere is thicker than Earth’s. Like Earth, it is mostly composed of nitrogen. It also has a hydrocarbon smog layer that obscures the surface from our view at visible wavelengths. This smog makes Titan look like a tangerine-colored ball. Look for this color in the telescope. Compare Titan’s color to the rings of Saturn. Does it look yellowish? You should also be able to spot Saturn’s next biggest moon, Rhea. If you look very carefully, you may be able to spot Dione and Tethys also. 

Objective:

To observe and map the atmospheric features of Saturn, its shape, its ring system, and at least two of its satellites (Titan and Rhea).

Requirements: A detailed sketch of the Saturn system made at the telescope, with the shape of the planet and rings correctly drawn, and Cassini's Division, and satellites labeled (if seen).

Directions:

1. Set up a telescope and align it with the north celestial pole. An accurate alignment is not required.

2. Find Saturn. Center Saturn in the eyepiece. Switch to high power.

3. Make an outline sketch of Saturn and its rings. Shade the ball of the planet a neutral gray so that light features can be sketched by erasing and dark features can be sketched by drawing darker.  Make the ball of the planet about the size of a quarter, so the rings will be significantly larger than this in your sketch.

4. Observe Saturn (without sketching) for about five minutes to let your eyes adapt to the subtle details on the surface of the planet, and look for faint moons that are visible.

6. Quickly sketch in the MAJOR details that you see on the surface.

7. Fill out the observing form (time, date, magnification, weather, seeing, etc.)

8. Now carefully fill in all of the tiny details that you can glimpse. Make notes of interesting features you see. Even the tiniest detail that you are sure of should be included. Be sure to record colors of the planet, rings, and moons. Also look for and accurately sketch the oblateness of Saturn.

9. Identify the moons that you see using the satellite diagram or sketch that your instructor provides for you.

Questions:

1. What is the orbital period of Saturn? How far is Saturn’s rotational axis inclined to its orbital plane? (Earth is inclined 23.5 degrees for comparison) How long is one season on Saturn? (one season lasts 3 months on Earth - but you already knew that, right?). Sketch how Saturn looks at its equinoxes and solstices.  What season was it on Saturn when you observed it?

2. What color were the rings? How did they form?  What are the rings made of?  Is this consistent with the color that you saw?

3. What color was the planet? What are the belts and zones?  Were they easy to see?  Why or why not (refer to a text book that compares Jupiter with Saturn in this regard).

4. What color was Titan?  What is so significant about its atmosphere?  What do these two things have in common?

5. How oblate is Saturn? To answer this question, measure the ratio of equatorial/polar diameters from your sketch.  Divide the equatorial diameter by the polar diameter and provide the answer.  Show your work. How does your measured oblateness compare with the actual oblateness of Saturn (refer to a text book and find the equatorial and polar diameters of Saturn and repeat the calculation using the real numbers).

6. Did you find Cassini’s Division? What causes this gap in the rings?  Could you see the cause of Cassini's Division in your telescope? 

7. How bright did Rhea, Dione, or Tethys appear compared to Titan?  Why (very easy answer)?